Terror latest: read more

Details of the thinking behind the high-profile defences came as it emerged today that a genuinely independent assessment of secret Government papers shows a real and present threat.

Lord Carlile QC, the leading barrister appointed by the Government to examine the fairness of the new emergency terrorism laws brought in after 11 September, made absolutely clear that there are both foreigners and UK citizens plotting terrorism.

"From the material I have seen, it is a certainty that there remain in the United Kingdom individuals and groups who pose a present and real threat to the safety of the public here and abroad," he said.

Meanwhile, Labour Party chairman John Reid got into a muddle today after comparing the danger facing London with 11 September.

Asked if the deployment of troops at Heathrow was an over-the-top reaction as a war against Iraq looms, he had angrily replied: "This is not a game. This is about a threat of the nature that massacred thousands of people in New York."

But he later downplayed his warning and claimed his original remarks had been "misinterpreted". Dr Reid told Radio 4's World At One: "It was precisely the suggestion that any government, this Government included, would use such a serious subject as international terrorism which gave us such things as New York for their own purposes of spin or public relations, I just found pretty contemptible.

"Now that was misinterpreted, I can understand why, by someone thinking that I had said that the scale of the threat at Heathrow was the same as the scale of the threat in New York. That was not meant. I am glad to have the chance to clear that up."

Find the latest advice on travelling to and from Heathrow here: www.baa.co.uk/main/airports/heathrow/